Umbrellas of the kind described above comprise a central post or support, a plurality of arms or ribs hinged to the upper end of the central post and spaced therearound, means for raising those arms or ribs from a collapsed position alongside the central post to an erected or open position in which those arms extend in radial array around the post to form the frame of the umbrella, a fabric canopy attached, usually removably so, to those arms or ribs, and means for locking or holding those arms in the extended or open position of the umbrella.
In one arrangement the means for erecting or opening the umbrella comprises a strut hingedly connected at one end to each rib at an intermediate point thereon and at the other end to a collar or ring positioned about and axially slidable along the central post or support. To open the umbrella the collar or ring is pushed upwardly to a position in which the struts support the ribs in open array. Releasable means are provided to lock the collar or ring in its upper position thereby to hold the umbrella in its open position.